NSTouch

An instance of the NSTouch class is a snapshot of a particular touch at an instant in time.
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A touch event is not persistent throughout the touch, new instances are created as the touch progresses. The identity property is used to follow a specific touch across its lifetime.

Touches do not have a corresponding screen location. The first touch of a touch collection is latched to the view underlying the cursor using the same hit detection as mouse events. Additional touches on the same device are also latched to the same view as any other touching touches. A touch remains latched to its view until the touch has either ended or is cancelled.